1. Field of the Invention
The present invention relates to a remote mechanical positioner for use with a thermal spray coating process. Radial and axial velocities and acceleration, parameters which are critical to uniform application of the coating, are controlled using programmed stepper motors. Recent applications of the thermal spray coating process include nuclear turbine cross-under piping. The positioning machine is modular and can be easily installed through a 12xc3x9718-inch manway opening typically found in the cross-under piping.
2. Background Information
Thermal spray coating has been a well-known useful technology for many years, as described in Thermal Spray Technology, xe2x80x9cEquipment and Theoryxe2x80x9d; R. W. Smith, Materials Engineering Institute, pp. 1-3 (1993), and includes combustion coating; plasma coating and electric/wire-arc coating. The primary application has been the coating of large digester tanks found in papermills. Recently, it has been thought useful for the inside of nuclear turbine cross-under piping for corrosion-erosion protection. Coating the inside of these pipes is, however, a very labor-intensive job. The surface to be coated must be first cleaned by conventional abrasive blasting to remove scale and surface contaminants. After this, a profile abrasive is pressure-blasted onto the surface to produce a whitemetal clean surface with a 0.0025 cm to 0.0127 cm (3 to 5 mil) anchor tooth profile surface finish. Once this is done, the surface must be thermal spray coated within four hours or an oxide (rust) will form on the surface inhibiting the bond quality of the thermal spray coating, which is typically a corrosion-erosion resistant material.
Thermal spraying, which includes plasma spraying and other coating processes such as combustion flame and electric/wire arc, is a well-known coating technique described, for example, in U.S. Pat. Nos.: 3,839,618; 4,649,858; 5,452,854; and 5,837,959 (Muehlberger; Sakai et al.; Keller; and Muehlberger, et al., respectively).
The person doing the thermal spray coating has to work on his knees inside a 91xc2xd cm (3-inch) diameter pipe wearing a blasting hood with a separate breathing supply. It is a physically demanding job that requires frequent rest periods, especially when the worker is abrasive blasting or thermal spraying overhead. Visibility is also a problem during either the abrasive blast-cleaning, profiling, or thermal spraying operations. The process generates a fair amount of smoke, and the actual thermal spray process literally produces a fountain of molten and particles, which are propelled against the surface to be coating using pressurized air or an inert gas. Approximately 20% of these molten particles wind up on the bottom of the pipe and must be cleaned up with a suitable vacuum cleaner.
Another problem with the manual application of a thermal spray coating concerns coating thickness. The goal is to apply a coating of uniform thickness over the whole area to be coated. When this is done manually, it is more difficult to achieve a uniform coating thickness. Measurements of the final coating thickness do show significant thickness variations when applied manually. An apparatus for cutting interior conduit surfaces and another for coating them are taught in U.S. Pat. Nos. 6,051,803 and 6,171,398 B1 (Hale and Hammer, respectively). Both teach rather complicated apparatus.
For the reasons above, there is a need to design and build a simplified remote application tool, which would allow remote application of the blasting, profiling, and thermal spraying operation. The main feature needed for the design is the ability to easily pass all parts of the machine through the 12xc3x9718-inch (30.5xc3x9745.7 cm) elliptical manway, and then assemble them in the cross-under pipe.
Therefore, it is a main object of this invention to provide an apparatus to coat the interior surface of hollow elongated conduits or pipes, which will allow application of thermal sprayed coatings, especially electric/wire arc coating, in cross-under pipes and the like.
These and other objects of the invention are accomplished by providing a machine for coating the interior surface of a hollow, axially elongated pipe characterized by comprising: a center portion of a support bar which can be aligned concentric with the centerline of the pipe; at least two tripods having at least three legs to contact the interior of the pipe and support the center portion of the support bar; at least one moveable carriage which can travel axially within the pipe, rotatably attached to the center portion of the support bar, said carriage containing at least one thermal spray coating device which extends from the carriage towards the interior of the pipe; a source of thermal sprayable material; a motor to drive the carriage axially; a motor to rotate the center portion of support bar and the carriage; a programmable controller external to the pipe which is capable of controlling the motors and thermal spray coating device. Preferably, all interior components of the coating apparatus are themselves protected, typically with an abrasion resistant plastic material. Also, the extension thermal spray device is adjustable in increments.
This provides a programmable thermal spraying apparatus for use in the interior of conduits such as axially elongated pipes that can be aligned concentric with the centerline of the pipe and which is adjustable and can coat the inside of the pipe. The same machine can also contain an abrasion cleaning/profiling head to first clean the pipe before coating it.